This research proposal is designed to investigate the development of the nervous system of the lungs of fetal, neonatal and adult rabbits and the effects of vagotomy on the neonatal rabbit lungs. The lung specimens include fetuses of gestational ages getween 15-31 days; and neonatal, mature and vagotomized rabbits. These lungs are studied with light and electron microscopy, as well as surfactant assay with bubble stability ratio and thin layer chromatography. The light microscopic localization of nerves includes the following techniques: silver impregnation, cholinesterase histochemistry and histofluorescence of adrenergic nerves. Electron microscopy is employed to study the fine distribution of the sensory and motor nerves and also to show the changes of nerves and cells of the lungs after vagotomy. The bubble stability ratio and thin layer chromatography can evaluate the degree of maturation or deficiency of the surfactant system in the developing or vagotomized lungs. The surfactant assay methods coupled with electron microscopic observations of the normal and vagotomized animals will provide additional information concerning the surfactant system, the activities of the type II pneumocytes and the roles of the nervous system in the development and the normal functions of the lungs.